Method and device for production of endless plastic hollow profiles

ABSTRACT

A method for production of endless plastic hollow profiles, in particular tubes, comprises several production stages for the plastic tube and a coating stage for a metal coating. A reduced pressure is provided in the coating stage, whereby the metal is transferred into the gas phase and deposited on the tube as a surface layer homogeneously bonded thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of producing endless plastic hollowprofiles, particularly tubes, as well as to a device for carrying outthe method, consisting of several production stages for the plastic tubeand a stage for application of an outer metal casing.

2. Description of Related Art

Coatings of plastic materials by means of thin-layer technology areknown particularly in the packaging industry. In that case a minimummetallic layer is applied at one side at high speed to a plastic film.This known method is not usable for the circumferential surface ofhollow profiles, particularly tubes, to which a layer with uniformthickness is to be applied, since in accordance with this method filmscan always only be coated at one side.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of creating, for hollowprofiles, a method by which a technically usable metal coating can beproduced in accordance with thin-layer technology at high productionspeed.

According to the invention this object is fulfilled in that the methodinvolves application of a liquid polymer to the surface of a tube andsubsequently a bonded metal layer is applied in a gas-tight layerthickness.

Refinements and developments of the invention are claimed in thesubclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

A device for carrying out the method is described as an example in thedrawings, in which:

FIG. 1 shows a schematic view of a coating plant, wherein the tubeissues from an extrusion plant,

FIG. 2 shows a schematic view of a coating plant, wherein the tube isunwound from a reel, and

FIG. 3 shows the schematic format of the coating stage.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A known device 1 for producing a plastic tube t, for example ofpolyethylene, consists of an extruder 11, a tool 12, a calibrating path13, a cooling path 14, a possibly desired printer 15, a withdrawal path16 for drawing the plastic pipe t in the direction of the arrow a, acutter 17 and a reel 18 for winding up very long pipe lengths.

According to the invention a system of three stations for coating theplastic tube t with a metal is inserted preferably between the coolingpath 14 and the printer 15.

The tube surface after exit of the tube t from the tool 12 is unevenwith a cratered form and in this state is not suitable for directcoating. The tube t therefore initially runs through a smoothing path 22in which a liquid polymer is applied to the tube surface. In thefollowing drying path 21 the applied polymer layer is dried. The tubesurface is thereafter suitable for coating.

Instead of application of a liquid polymer, the tube surface can also besmoothed by exposure to flame.

Subsequently, the thus-pretreated tube t runs through the coating path2. The internal format of the coating path 2 is illustratedschematically in FIG. 3. Disposed in the interior of the coating path 2are, for example, four flame treatment modules 231, 232, 233, 234, whichare displaced relative to one another in each instance by an angle of 90degrees so that a uniform coating of the tube t takes place. However, itis also possible to mount the modules to be movable and to let themcirculate around the tube t during the coating. The flame treatmentmodules are electrically heated and evaporate the coating metal, forexample aluminium or copper, so that this is transferred into the gasphase and deposits on the tube t. An underpressure preferably prevailsin the coating path 2. Due to the very smooth surface of the tube t,expensive sealing measures are not necessary.

A liquid lock, as is known for vacuum containers in continuousproduction processes, would also be highly disadvantageous for coatingin vacuum, since the surface of the tube if wetted by the liquid is nolonger capable of being coated. The seals 241, 242 are therefore plasticseals of resilient material.

In the afore-described device 1 it is necessary to design the differentlengths of the smoothing path 22, drying path 21 and coating path 22transited by the tube t so that these can fulfil their tasks at thepreset production or extrusion speed.

In FIG. 2 there is reproduced a device 1 in which the tube t to becoated is already present and wound up on a reel 18. It then runsthrough only the paths 22, 21, 2. In this case the transit speed throughthe paths 22, 21, 2 is no longer dependent on a production speed, butcan be designed exclusively in accordance with the requirements of thethree paths 22, 21, 2.

It is feasible to combine the three paths 22, 21, 2 into a unit. In thiscase only two seals are required.

Reference Numeral List 1 device 11 extruder 12 tool 13 calibrating path14 cooling path 15 printer 16 withdrawal path 17 cutter 18 reel 181 reel2 coating path 21 drying path 22 smoothing path 231 flame-exposuremodule 232 flame-exposure module 233 flame-exposure module 234flame-exposure module 241 seal 242 seal t plastic pipe a arrow of themovement direction

1. A method of continuously producing an endless plastic hollow productcomprising: feeding said endless plastic hollow product; initiallysmoothing an outside surface of said plastic hollow product by applyinga liquid polymer to an outside surface of said plastic hollow product asit is fed; and thereafter, applying a metal to the liquid polymer-coatedplastic hollow product as it is fed, wherein said metal layer uniformlyand intimately connects with the liquid polymer layer in a mutuallygas-tight layer thickness.
 2. The method as set forth in claim 1,wherein said metal layer applying step comprises evaporating metal froma plurality of metal evaporation units disposed circumferentially aboutsaid plastic hollow profile product as said product is moved.
 3. Themethod of claim 2, wherein said applying step is conducted bycirculating a plurality of said units about said plastic hollow profileas it is moved.
 4. The method of claim 1 wherein said evaporation stepis conducted in an under-pressure environment.
 5. The method of claim 1further comprising drying said polymer after said coating step andbefore said applying step.
 6. A system for producing endless plastichollow product comprising: a feeder for feeding said productcontinuously; a smoothing unit for coating said endless plastic hollowproduct with a liquid polymer as said product is fed; and a metalapplying unit for transferring in a gas phase and in an underpressureenvironment a metal onto the polymer-coated endless plastic hollowproduct, whereby said metal is intimately bonded as a layer in agas-tight layer thickness.
 7. The system as set forth in claim 6 furthercomprising a plurality of evaporation units located within said applyingunit and disposed about different circumferential surface portions ofsaid plastic hollow product as it is fed.
 8. The system of claim 7wherein said plurality of evaporation units are circulated about thecircumference of said plastic hollow product as it is fed.
 9. The deviceas set forth in claim 6 further comprising a drying unit disposedbetween said polymer coating unit and said metal applying unit.
 10. Thesystem of claim 6 wherein said metal applying unit is sealed andcomprises a housing and at least one port, having resilient materials,through which said plastic hollow product is fed.